The present invention relates to the field of apparatus for surface treatment by impact.
It is known that a metal part can be treated by steel shot blasting for the purpose of hardening the part, for example.
Shot blasting can be performed under the effect of a jet of compressed air from a shot blaster.
The drawback of such a blaster is that it requires a large supply of shot and it is usable only in a space that is adapted to recovering the shot that has rebounded from the part.
Apparatuses for surface treatment by impact are also known in which the shot is projected by means of a sonotrode placed in the bottom of a metal bowl whose mouth is positioned in register with and at a small distance from the surface to be treated.
Apparatuses of that type present the advantage of the shot returning after rebounding on the part to the sonotrode so as to be projected again against the surface to be treated.
There is thus no loss of shot, providing the clearance between the bowl and the part being treated is small enough to ensure that none escapes.
In order to start the shot moving, it is necessary to bring the shot into contact with the sonotrode, and that presents difficulties when the mouth of the bowl needs to be directed downwards in order to treat the part.
In addition, because of the risk of shot being lost if the clearance between the treated part and the bowl is increased, e.g. when the bowl is moved, such treatment is banned in a regulated environment, such as in the nuclear industry.
Consequently, there exists a need for apparatus to be made available for performing surface treatment by impact and that remedies the above-mentioned drawbacks in particular.
The present invention provides novel apparatus for surface treatment by impact, the apparatus being of the type comprising a vibrating surface and at least one projectile suitable for being projected towards the surface to be treated by said vibrating surface, the apparatus including retaining means for holding each projectile captive in the apparatus when said apparatus is moved away from the surface to be treated.
By means of the invention, it is easy to treat the surface of a part by impact without running the risk of losing shot or without any problem of consuming shot, unlike the previously known apparatuses mentioned above.
The projectiles are advantageously held captive by the apparatus independently of the surface to be treated.
In a particular embodiment, the apparatus includes guide means for guiding each projectile in its forward movement and after rebounding on the vibrating surface.
Thus, when a plurality of projectiles are used, it is possible to guide them in such a manner as to prevent them colliding with one another and to optimize the trajectories of the projectiles between the vibrating surface and the surface to be treated.
In a particular embodiment, the apparatus includes drive means for displacing the guide means relative to the remainder of the apparatus.
Advantageously, the drive means make it possible to make the distribution of the impact points on the surface to be treated uniform and to make the wear of the sonotrode uniform.
In a particular embodiment, each projectile slides in a guide means.
In another particular embodiment, each projectile pivots about an axis between a position in which it comes into abutment against the vibrating surface and a position in which it comes into abutment against the part to be treated.
Still in a particular embodiment, the apparatus includes return means for initiating the motion of each projectile by bringing it into contact with said vibrating surface regardless of the orientation of the apparatus.
In a particular embodiment, the return means comprise at least one chamber into which air can be delivered or from which air can be sucked to urge each projectile towards the vibrating surface.
In a particular embodiment, said retaining means are organized to allow each projectile to strike directly the surface to be treated.
In a variant embodiment, the retaining means are organized to receive the kinetic energy from each projectile and to transfer it locally to the surface to be treated.
By way of example, the mass of each projectile lies in the range 0.1 grams (g) to 5 g.
The invention presents the advantage of making it possible to use a small quantity of projectiles.
Thus, for example, it is possible for the projectiles to use high quality balls of the kind used in ball bearings. Projectiles of this type make it possible to guarantee that the desired material effects are controlled and reproducible.
In a particular embodiment, the apparatus includes a plurality of projectiles each in the form of a pin or slug, together with guide means in the form of a guide piece having a plurality of housings for slidably guiding said pins or slugs.
The term xe2x80x9cslugxe2x80x9d is used to designate an optionally stepped cylinder with one or both ends being rounded in substantially hemispherical manner without any flat zone.
A ball can be considered as being a slug having generator lines of zero length.
In a particular embodiment, each pin or slug is provided with a shoulder and each housing in the guide piece has a shoulder serving as an end-of-stroke abutment for the associated pin or slug.
In a particular embodiment, the guide piece has a chamber organized to deliver compressed air to the fronts of the shoulders of the pins or slugs and to urge them back towards the vibrating surface.
For example, said chamber is defined at its rear by the body of the guide piece and at its front by a perforated cover fitted to the body of the guide piece.
In a particular embodiment, the guide piece is mounted to rotate about an axis parallel to the sliding direction of the pins or slugs.
Still in a particular embodiment, the pins or slugs are made by inserting rods into sleeves of shorter length than the rods.
In a variant, the pins or slugs consist in single pieces.
In another particular embodiment, the retaining means are constituted by a carpet of beads and the apparatus includes at least one projectile constituted by a ball that is free to rebound successively between the vibrating surface and the carpet of beads.
Preferably, the carpet of beads has beads mounted with clearance on support wires.
In another particular embodiment, the retaining means are constituted by pins or slugs that are movable in a dome-shaped wall, each pin or slug having an end suitable for striking the surface to be treated, the projectiles being constituted by balls that are guided in channels so as to perform back-and-forth motion between the vibrating surface and the other ends of the pins or slugs.
In a particular embodiment, the projectiles are held captive by a guide assembly removably mounted on the apparatus, thereby making it easy to change the projectiles as a function of the surface to be treated.
In a variant embodiment, the apparatus includes an enclosure that is open towards the surface to be treated and the retaining means comprise means serving to generate suction in said enclosure when the enclosure moves away from the surface to be treated by more than a predetermined distance, thereby sucking in the projectiles and preventing them from leaving the apparatus.
Thus, the projectiles do not leave the apparatus.
Advantageously, the apparatus includes a recovery chamber for the projectiles, which chamber is in communication with the enclosure and into which the projectiles are sucked when the enclosure moves away from the surface to be treated by more than a predetermined distance.
Preferably, the apparatus further includes means enabling the balls contained in the recovery chamber to be expelled into the enclosure when the enclosure is close enough to the surface to be treated to ensure that the projectiles are prevented from escaping therefrom.
In a particular embodiment, the edge of the enclosure that comes into register with the surface to be treated is provided with at least one detector suitable for changing state when the distance between the enclosure and the surface to be treated passes through a predetermined value.
Preferably, the edge of the enclosure is provided with a plurality of detectors so as to ensure that the enclosure is sufficiently close to the surface to be treated around its entire periphery at the time the projectiles are sent into the enclosure.
The invention also provides portable apparatus for performing surface treatment by impact, the apparatus including a sonotrode and a plurality of projectiles in the form of pins or slugs slidably mounted (optionally separately) in a guide piece, the guide piece being secured to handle means enabling the user to position it manually to face the part to be treated, the guide piece being organized and positioned relative to the sonotrode so as to enable the pins or slugs to perform back-and forth motion between the sonotrode and the part to be treated by rebounding successively thereon, and secondly to retain the pins or slugs in the absence of a part to be treated.
Such apparatus makes it easy to treat a part in situ, without any fear of losing shot, which is most advantageous compared with known apparatuses.
The invention also provides a set of projectiles for apparatus as defined above.
The invention also provides the use of apparatus as defined above for modifying in situ the shape of a part in order to enable it to be integrated in an assembly.
The invention also provides the use of apparatus as defined above for performing surface treatment in situ and for creating a specific surface state. By way of example, the treatment can consist in treating a cracked part that has been repaired by adding material or in rectifying boiler plate very quickly, or indeed in shaping such a part.
The invention applies to treating all types of part subjected to mechanical stress such as engine parts, structural parts, connection parts, or welded assemblies.